The present invention relates to a feeler pin and a feeler head for coordinate measuring machine.
Coordinate measuring machines are generally known in the prior art. They serve for measuring test objects, for example in quality assurance. It is possible in principle to make use of various sensor systems to detect the coordinates of the test object. By way of example, it is customary to use optical sensors, but in particular also tactile sensors which sense selected points of the test object and determine the coordinates of the scanned point.
For this purpose, a coordinate measuring device has a feeler head in which there is located a sensor arrangement which can detect a deflection of a feeler pin which scans the test object with the aid of a feeler object. Previously determined calibration data can be used to determine from the sensor signals the position of the feeler object relative to the feeler head, and also to determine the coordinates of the sensed point on the basis of the known position of the feeler head in the coordinate measuring machine.
Depending on the geometry of the test object, it can be required in some circumstances to change the feeler pin during a test operation. For example, it can be required to make use of a feeler pin which is thinner, thicker or bent, or else of a feeler object of different shape. The feeler objects can, for example, be designed as a ball or else as a cylinder.
To date, it has been necessary each time when changing the feeler pin to carry out renewed calibration of the feeler pin and/or the coordinate measuring machine in order to be able to draw an exact conclusion on the coordinates of the scanned point from the sensor signals. However, in the prior art methods have also been proposed for calculating the calibration data of a specific feeler pin in advance, and storing them in the coordinate measuring machine. If the coordinate measuring machine then later makes recourse to this feeler pin, it is then possible to appeal to these calibration data without renewed calibration.
However, this requires that the coordinate measuring machine be able to completely identify the feeler pin used. It has been proposed for this purpose in the publication US 2008/0052936 A1 to provide the feeler pin with an identification chip which can be read out via the feeler head. For this purpose, data via which the feeler pin can be uniquely identified are stored in the identification chip.
Possibilities for wireless as well as wired connections are specified in the prior art for the use of the identification chip with the coordinate measuring machine.
Thus, for example, publication DE 10 2006 033 443 A1 exhibits a feeler pin with an integrated RFID chip for the wireless connection of the identification chip, configured as an RFID chip, to the coordinate measuring machine. Such wireless connection methods require, for example, an autonomous energy supply inside the feeler pin, for example by means of a battery.
In the case of wired identification chips, it is possible for them to be included in a circuit via the connection, and thus to be read out without a dedicated energy supply. For this purpose, the identification chip can be configured as, for example, a read only memory which, once it has been written to, retains the stored data even without energy supply. However, this requires provision of suitable contacts. It is to be ensured in this case that any possible current flow does not corrupt the measurement results.
The publication EP 1 643 208 A2 proposes to provide the contacts via the bearings of the feeler pin plate in the feeler head.
As a rule, a feeler pin has a fastening sleeve which can, in particular, have an external thread. This fastening sleeve is used to screw the feeler pin into the feeler head. A particular thread diameter can be required for this purpose depending on the feeler head used. However, since the feeler pins are the same as a rule, feeler pins of the same design with different fastening sleeves are provided which can differ from one another depending on the type of fastening and dimensioning.
In order to simplify the production of such feeler pins, it has been proposed to connect a shaft of the feeler pin which supports the feeler object, for example a feeler ball, to the fastening sleeve by means of an injection moulding method. The injected plastic in this case insulates the fastening sleeve and the shaft from one another electrically thus resulting in new possibilities and requirements for providing such a feeler pin, which has an identification chip, with contacts.
Furthermore, by way of example the contacts described in the US 2008/0052936 A1 mentioned above have a specific orientation which is to be observed for the purpose of making a secure contact. Consequently, this publication proposes a pin which latches tight in a specific orientation and thus ensures secure contact with the feeler pin in the feeler head. Thus, secure contact is obtained only in a specific position of the feeler pin relative to the feeler head.